Quantification of the relation between surface morphodynamics and subsurface sedimentological product in sandy braided rivers

This study uses digital elevation models and ground‐penetrating radar to quantify the relation between the surface morphodynamics and subsurface sedimentology in the sandy braided South Saskatchewan River, Canada. A unique aspect of the methodology is that both digital elevation model and ground‐penetrating radar data were collected from the same locations in 2004, 2005, 2006 and 2007, thus enabling the surface morphodynamics to be tied explicitly to the associated evolving depositional product. The occurrence of a large flood in 2005 also allowed the influence of discharge to be assessed with respect to the process–product relationship. The data demonstrate that the morphology of the study reach evolved even during modest discharges, but more extensive erosion was caused by the large flood. In addition, the study reach was dominated by compound bars before the flood, but switched to being dominated by unit bars during and after the flood. The extent to which the subsurface deposits (the ‘product’) were modified by the surface morphodynamics (the ‘process’) was quantified using the changes in radar‐facies recorded in sequential ground‐penetrating radar surveys. These surveys reveal that during the large flood there was an increase in the proportion of facies associated with bar margin accretion and larger dunes. In subsequent years, these facies became truncated and replaced with facies associated with smaller dune sets. This analysis shows that unit bars generally become truncated more laterally than vertically and, thus, they lose the high‐angle bar margin deposits and smaller scale bar‐top deposits. In general, the only fragments that remain of the unit bars are dune sets, thus making identification of the original unit barform problematic. This novel data set has implications for what may ultimately become preserved in the rock record.     

Estuarine deposition of a mid-Viséan tetrapod unit,Ducabrook Formation,central Queensland: implications for tetrapod dispersal

At Ducabrook property, central Queensland, the mid-Viséan Ducabrook Formation has yielded a diverse vertebrate fauna (fish and one tetrapod taxon) from a thin unit among siltstone interbedded with sandstone, minor oolitic limestone and conglomerate. Five lithofacies can be distinguished: the Oolitic Facies, distinguished by oolitic limestone and straight parallel ripple crests; the Sandy Facies, composed of plane-laminated and current-rippled sandstones; the Conglomeratic Facies, represented by pebble conglomerate displaying planar cross-bedded megaripples; the Silty Facies of siltstone with abundant calcrete nodules or sand/silt/clay interlaminations; and the Lime-Flake Facies, characterised by abundant locally derived lime flakes. The last includes the fossiliferous tetrapod unit. The Oolitic Facies was deposited in the inner (proximal) and outer (distal) zones of an estuary, based on identification of tidal sedimentary structures (e.g. mud drapes) and estuarine oolitic fabrics; the Lime-Flake Facies and Silty Facies were deposited in the estuary and lower reaches of a river and its surrounds; and the Sandy and Conglomeratic Facies represent braid-river deposits. Overall, the sequence represents intermittent deposition throughout an estuary, both within the tidal channel and the surrounding tidal flats, with additional deposition from the feeder river. The tetrapod unit, from the Lime-Flake Facies, represents a twin-peaked storm-induced flood event onto the tidal channel floor. The vertebrate bones have a shared taphonomic history and have undergone only local transport. The tetrapod and fish were spatially and temporally concurrent, probably in a shallow tidally influenced proximal estuarine habitat experiencing monsoonal conditions. Estuarine adaptations of these vertebrate taxa can explain migration along shallow-water continental shelves between the supercontinents during the Late Devonian and Early Carboniferous.     

Sea level trends at locations of the United States with more than 100?years of recording

The paper presents the sea level rises (SLR) computed for the United States tide gauges with more than 100?years of recording. It is shown that the monthly sea levels oscillate about an almost linear longer-term trend with important multidecadal periodicities. The SLR time history is computed by linear fitting of 20, 30 and 60?years of data up to a given time (SLR₂₀, SLR₃₀ and SLR₆₀) and is compared to the value obtained by considering all the data. It is shown that SLR₆₀ has smaller oscillations, while SLR₂₀ and SLR₃₀ have much larger and frequent fluctuations. While SLR₆₀ may oscillate ±10?C30?% about the latest longer-term value, SLR₃₀ may fluctuate ±50?C100?% and SLR₂₀?±?100?C200?%. The values obtained by considering all the data with a minimum of 60?years (SLR_A) also fluctuate ±5?C15?% about the latest longer-term value. This indicates the need to use the time history of SLR₆₀ or SLR_A when the record is longer than 60?years to assess the accelerating trend. For all the stations, the sea levels regularly oscillate about the linear longer-term trend, and if acceleration has to be computed, this is eventually negative, that is, the SLR is reducing.     

Comparison of low-energy lunar transfer trajectories to invariant manifolds

In this study, transfer trajectories from the Earth to the Moon that encounter the Moon at various flight path angles are examined, and lunar approach trajectories are compared to the invariant manifolds of selected unstable orbits in the circular restricted three-body problem. Previous work focused on lunar impact and landing trajectories encountering the Moon normal to the surface, and this research extends the problem with different flight path angles in three dimensions. The lunar landing geometry for a range of Jacobi constants is computed, and approaches to the Moon via invariant manifolds from unstable orbits are analyzed for different energy levels.     

Second-Hand Spaces: Restructuring Retail Geographies in an Era of E-Commerce

Are online markets replacing or remaking second-hand markets in cities? The restructuring of secondary markets in light of virtual outlets like eBay is not well understood. In this article, we describe secondary markets and their important historic, economic, cultural, and social roles in cities. The literature on e-Commerce suggests that virtual retailers compete with bricks-and-mortar stores and potentially displace them. We question whether the internet can substitute for second-hand stores, which have traditionally relied on a loyal and local customer base, personalized shopping experiences, and surprise encounters. Given the historically embedded nature of exchange, we focus on one large Mid-western city, drawing upon survey and interview data from Chicago retailers. Our exploration of supply, demand, and geographic practices reveals subtle and complex alterations in second-hand exchange, rather than a displacement of second-hand markets by eBay. We also find substantive integration, fluidity, and hybridization within and across market sectors. Rather than supplant the production of new goods, secondary markets are intertwined with and deepen primary markets, calling into question some of the presumed benefits of and meanings associated with second-hand exchange as well as the usefulness of categorical distinctions. [Key words: secondary markets, second-hand, resale, thrift, e-commerce, eBay.]     

SYNOPTIC CONTROL OF REGIONAL TEMPERATURE TRENDS IN THE COTERMINOUS UNITED STATES BETWEEN 1949 AND 1981

Regional patterns of January and mean annual temperature change between 1949 and 1981 are compared with regional changes in January precipitation totals and related to upper-level atmospheric circulation. During cold periods, cooling is concentrated in the eastern United States and is associated with a southward shift in the zone of maximum precipitation in the eastern United States (reflecting the mean position of the polar front jet), and with a strengthening of meridional flow aloft. During this same period, enhanced meridionality yields an increase in temperatures in the Pacific Northwest, associated with amplification of the mean long wave ridge over the Rocky Mountains. Warm periods in the eastern United States, conversely, correlate with a stronger zonal flow aloft (resulting in cooler, wetter conditions in the Pacific Northwest). Accordingly, temporal variation in regional temperature trends may be more readily interpreted as responses to synoptic controls which yield departures of opposite sign in locales influenced by ridges vs. troughs, rather than as a reflection of uniform, progressive hemispheric or global temperature change.     

COMPOSITIONAL GRADIENTS IN MESOPHYTIC FORESTS OF EASTERN NORTH AMERICA

Numerical classification and ordination techniques are used to examine compositional variability in 112 stands of mesophytic upland forest in the eastern United States from data published by Braun (1950). Five forest types are identified and used to interpret ordination results. Two prominent environmental gradients account for much of the compositional variability in the data set: along the first ordination axis a microclimate gradient reflects increasing soil moisture availability and cold stress from dry uplands to northern hardwood sites; along the second ordination axis, a soil fertility gradient segregates hemlock coves and dry uplands, both of which are characteristically found on shallow, nutrient-poor soils, from the other forest types. The efficacy of combining numerical classification and ordination techniques for analyzing and interpreting patterns in ecological data is underscored by these results.     

CLIMATOLOGY OF STATEWIDE EXTREME TEMPERATURES DURING WINTER MONTHS IN THE COTERMINOUS UNITED STATES

A 20-year (1961-1980) record of statewide extreme maximum and minimum temperatures for the winter season is examined for the coterminous United States. Extreme maxima exhibit a zonal pattern, modified somewhat by terrain features in the west. Extreme minima are more dramatically skewed from a zonal orientation, because of the effects of elevation and proximity to oceans. Interannual variability in the record of extreme temperatures appears to be dictated by proximity to air-mass source regions (e.g., low variability of minima in the Upper Midwest, low variability of maxima in the Deep South) and sensitivity to the position and amplitude of mid-tropospheric circulation and snowpack dynamics (e.g., high variability of minima in the Ohio Valley). Strong, spatially coherent patterns of correlation between statewide extremes and amplitude of midtropospheric flow are evident (negative correlation with enhanced troughing in the east; positive correlation with enhanced ridging in the west). Lag correlations with ENSO indices suggest a relatively weak linkage between antecedent conditions in the Pacific and the degree of extremeness of maximum (but not minimum) temperatures in the eastern United States. [Key words: extreme maximum temperatures, extreme minimum temperatures, climatic variability, meridionality indices, El Nino-Southern Oscillation, snowpack.]     

Characterization of Persistent Volatile Contaminant Sources in the Vadose Zone

Effective long‐term operation of soil vapor extraction (SVE) systems for cleanup of vadose‐zone sources requires consideration of the likelihood that remediation activities over time will alter the subsurface distribution and configuration of contaminants. A method is demonstrated for locating and characterizing the distribution and nature of persistent volatile organic contaminant (VOC) sources in the vadose zone. The method consists of three components: analysis of existing site and SVE‐operations data, vapor‐phase cyclic contaminant mass‐discharge testing, and short‐term vapor‐phase contaminant mass‐discharge tests conducted in series at multiple locations. Results obtained from the method were used to characterize overall source zone mass‐transfer limitations, source‐strength reductions, potential changes in source‐zone architecture, and the spatial variability and extent of the persistent source(s) for the Department of Energy's Hanford site. The results confirmed a heterogeneous distribution of contaminant mass discharge throughout the vadose zone. Analyses of the mass‐discharge profiles indicate that the remaining contaminant source is coincident with a lower‐permeability unit at the site. Such measurements of source strength and size as obtained herein are needed to determine the impacts of vadose‐zone sources on groundwater contamination and vapor intrusion, and can support evaluation and optimization of the performance of SVE operations.